libdw: Skip zero entries in aranges

libdw: Skip zero entries in aranges

An address/length entry of two zeros is supposed to mark the end of a
table. But in some cases a producer might leave zero entries in the
table (for example when using gcc -ffunction-sections -gc-sections).

Since we know the lenght of the table we can just skip such entries
and continue to the end.

    * libdw/dwarf_getaranges.c (dwarf_getaranges): Calculate endp.
    When seeing two zero values, check we are at endp.

https://sourceware.org/bugzilla/show_bug.cgi?id=27805

Signed-off-by: Mark Wielaard <mark@klomp.org>